Field of the Invention
The present invention relates to rotary x-ray tubes, and in particular to such an x-ray tube for producing stereo x-ray exposures.
2. Description of the Prior Art
Stereoscopic x-ray tubes are known in the art generally including an evacuated housing having a motor-driven anode therein, and at least two cathodes which are directed to at least two foci within at least one track of the anode dish disc or plate. Two alternating beams of useful x-rays are thereby generated and directed toward an examination subject. For generating stereo x-ray exposures, the spacing between the foci may, for example, correspond to the distance between the pupils of an average viewer. X-ray exposures produced in this manner are then observed with a reproduction means for stereo images.
A stereo x-ray system is described in German Pat. No. 21 57 843, corresponding to U.S. application Ser. No. 302,546 filed Oct. 31, 1972 (Duemmling), now abandoned. This system includes two separate x-ray tubes disposed at a slight distance next to each other, which are alternately supplied with high voltage. The minimum possible spacing of the two foci is thus determined by the tube dimensions, and thus frequently cannot be selected small enough. A substantial circuit outlay is also required, given a high frame frequency, because the two x-ray generators are necessary and must be alternatingly switched.
A stereo tube is also described in a data sheet published by Siemens AG for its Stereolix.RTM.Unit wherein the foci are broght to the two different positions required for stereo imaging by means of mechanical motion of a single cathode. The frame frequency is limited in this unit by the inertia of the motion.
When higher frame frequencies are required, an x-ray tube having a plurality of cathodes must be employed. The cathodes are alternatingly switched by means of a grid control as described in German OS No. 14 89 114, corresponding to U.S. Pat. No. 3,250,916. This arrangement also requires considerable circuit outlay because the control voltages, given the symmetrical high-voltage of the x-ray tubes which is normally employed, must be greater than one half of the high-voltage.
A computer tomograph system is described in German OS No. 31 12 016 wherein a plurality of slices can be simultaneously transilluminated and wherein a plurality of focal points in different anode tracks are generated on the anode dish, with an x-ray beam proceeding from each focal point. Only one detector row is provided for acquiring the x-rays. In order for a corresponding allocation of the output signals of the detector row to be made, the focal point tracks on the anode dish are in the form of segments consisting of a material which does not emit x-radiation, such as plastic. A periodic, chronologically coded interruption of the x-ray beam is thereby achieved, with every x-ray beam associated with a particular slice being given a different coding. The association of an output signal of the detector row with a given slice can be subsequently identified by the coding, so that the signals can be separately stored. A periodically alternating, uniform switching of two x-ray beams required for stereo techniques is not achieved by this system.